Brennan Center Overview of Voting Equipment

This is the Brennan Center's resource page describing different categories of voting equipment.

May 31, 2018

Optical/Digital Scan Paper Ballot Systems require voters to mark paper ballots, which are subsequently tabulated by scanning devices (“scanners” or “scan systems”). The scanners optically or digitally sense the markings on the inserted ballot and these marks are used for tabulation.

Generally, voters select the candidate of their choice on optical/digital scan paper ballots by filling in an oval (on ES&S, Dominion, Premier/Diebold and Unisyn ballots), completing an arrow (Sequoia ballots), or filling in a box (Hart Intercivic ballots). These formats are considered traditional paper ballot formats. As completing-the-arrow ballot formats have had higher rates of residual votes, and substantially higher rates of overvotes, they should be avoided in favor of “complete-the-oval” ballot formats. 

Once marked, ballots may be scanned on optical/digital scan systems in the polling place (known as “precinct count”) or collected in a ballot box or otherwise centrally aggregated, e.g., vote-by-mail ballots, to be scanned at a central location (known as “central count”). Precinct count scanners must provide voters notice of overvotes (where voters select too many candidates, thus spoiling the ballot for that contest) and should automatically return overvoted or otherwise erroneous ballots to the voter for correction. Central count scanners, generally used for mail ballots, do not have this functionality as the voter is not present when the ballot is scanned for tabulation purposes. 

Examples include:, Dominion ImageCast Models Precinct, Evolution and Central; ES&S Models 100, 150, 550, and 650; Sequoia-branded and ES&S-branded Optech III-P Eagle; Sequoia Optech Insight and Optech 400C; Premier/Diebold (Dominion) AccuVote-OS and OSX; and Unisyn OVO.


Ballot Marking Device (“BMD”) systems produce a marked ballot (usually paper) that is the result of voter interaction with visual or audio prompts provided by a computerized interface. The result is a voter-verifiable ballot that may or may not be accessibly verified. These systems are most often used in combination with the optical/digital scan systems discussed above.

Some BMDs produce a paper ballot that uses a traditional paper ballot format. Other BMDs produce a paper ballot that simply includes a list of the voter’s choices and a QR code or a bar code, but is not printed in a traditional ballot format and does not include human readable markings. For both, voters take the ballot and separately insert the ballot into a scanner. For traditional paper ballots, the scanner uses the human-readable marks on the ballot to tabulate votes. If the ballot includes a QR code or a bar code, the scanner uses these marks to tabulate votes. States that certify code-generating BMDs should also mandate that, if the ballot includes a QR or a bar code, it must also include a human-readable list of selections, and that only the human-readable portions of these ballots may be used during audits and recounts. These requirements will ensure that each vote is properly tabulated as cast and that errors in the programming of the BMD’s code generator or the scanner tabulation system are detected. 

Still other BMDs count votes internally (as do DRE systems) and may save voter selection information. For any BMD that does count, save, or use cryptography or other techniques to make it difficult to insert fraudulent ballots prepared on other devices (before, during or after actual voting), any discrepancy between records stored within a BMD and physical ballots produced would provide clear evidence of malfunction or fraud and initiate an investigation to determine the source of the discrepancy and the invalid ballots, whether electronic or physical. Examples of BMDs include: AutoMark and Populex.

There are many reasons a jurisdiction will want to purchase ballot marking devices, but among the most important is federal law.  Every polling place that uses optical scan equipment must have at least one BMD that allows voters with disabilities to vote independently and privately, as other voters do.

BMDs offer many useful features beyond satisfying federal requirements to accommodate voters with disabilities. By offering a “read-aloud” feature, BMDs enable voters with limited reading skills in the ballot language or visual impairments to have the ballot read to them on headphones. BMDs are also able to efficiently provide ballots in alternative languages. In addition, BMDs can improve the accuracy of voters’ intentional markings on paper ballots, including elderly voters and those with hand tremors.


Direct Recording Electronic (“DRE”) voting systems directly record, in electronic form, the voters’ selections in each race or contest on the ballot. Typical DRE machines have flat panel display screens with touch-screen input, although other input technologies have been used, such as push-button. Such systems can be compared with mechanical lever voting machines which directly record votes on mechanical counters inside the machine.

The defining characteristic of DRE machines is that votes are captured electronically and stored in that form. Such machines may print a durable paper record of the votes cast, for example, after the polls are closed or on an internal printer, but this record is not subject to voter verification. DRE machines also record Event Logs giving the time of each significant operation on the machine, such as when it was set up for an election, when the polls were opened, when the polls were closed, and when a ballot was cast (but not which ballot was cast). At the close of polls, vote totals, the Event Log, and all votes cast may be printed. In

addition, electronic records of these may be extracted from the machine (for example, on removable media such as disks or compact electronic memory modules), or the records may be transmitted electronically to a vote collection center (for example, by modem).

Procedures for using these alternatives vary from jurisdiction to jurisdiction. Typically, the electronic transmission or the electronic memory module is delivered to a central vote-counting system (for example, in the county election headquarters), where jurisdiction-wide totals are computed. There are three subtypes of DRE machines, based on the style of user interfaces/interaction:

1. The scrolling DRE uses a touch-screen to collect user input (when not in an audio ballot mode) and typically allows voters to page through separate screens for separate offices. Examples include: Sequoia AVC Edge, the ES&S iVotronic, Premier/Diebold (Dominion) AccuVote-TS and -TSX, AVS WinVote, and.

2. The full-face DRE has no paging, and it generally involves an electromechanical human interface, which uses switches providing tactile feedback to the voter. (The Avante DRE does produce a full-face ballot that uses a touch-screen) Examples include: Sequoia AVC Advantage and Danaher Shouptronic/ELECTronic 1242.

3. DREs with off-screen mechanical control allow the user to view options displayed on a screen but provides input via buttons, switches, dials or other input devices. Examples include: Hart InterCivic’s eSlate.


DREs with Voter-Verifiable Paper Trails (“DRE w/ VVPT”) capture voter choices internally in purely electronic form and contemporaneously on paper in a record that can be verified by the voter. The paper record is usually not physically handled by voters, and it remains at the polling place, mechanically stored

within or near the DRE machine used to cast the vote. DREs w/ VVPT include those that ensure voter privacy by automatically separating and randomizing vote selections for storage and those with reel-to-reel designs. Examples include: Dominion ImageCast X and AccuVote TSX; ES&S iVotronic; and Sequoia AVC Edge.

DREs without VVPT do not create a tangible physical record of the voter’s selections on a physical ballot.